Kahneman and Caloric Leakage

In a recent post, I discussed Daniel Kahneman's Thinking Fast and Slow, a very interesting book. Part of its point is that much, arguably most, of our thinking is done by a part of our mind that functions, invisibly and automatically, in the background, the part that recognizes faces and facial expressions, voices, and much else, a part that is very fast but not very smart. Many of the errors we make are due to the limitations of that part of our mind, limitations that are an almost inevitable accompaniment to its speed. 

Thus, for example, the fast mind, faced with a problem it does not know how to solve, substitutes a similar problem that it does know how to solve and offers the solution to the second question in place of a solution to the first—without mentioning to the slow mind, the part that is responsible for rational thought, that it has made the substitution. Another limitation of the fast mind is that it is very bad at fine distinctions; thus, for example, it tends to deal with probabilities by classifying them into one of three categories—impossible, possible, certain. Attention, processing by the slow mind, is a scarce resource, so most of the time the slow mind simply accepts the information fed to it by the fast.

It occurs to me that the malfunctions of the fast mind may help explain why it is so hard to lose weight. Consider the well known principle of caloric leakage, the principle that holds that although a cookie has lots of calories, a piece of a broken cookie does not, the calories having leaked out—so you might as well eat it. Or consider my well established weakness for marginal cost zero food—another serving at an all-you-can-eat buffet.

The explanation for caloric leakage is the inability of my fast mind to deal with fine distinctions—a piece of a cookie is entirely different from a cookie, cannot be viewed as half a cookie, and so my knowledge that it has half the calories of the cookie never gets triggered. The explanation for the second problem is that, faced with zero marginal cost food, I have no need to pass the decision of whether to eat it on to my slow mind to decide whether it is worth the cost in money—and my fast mind doesn't worry about the cost in calories. 

Also, as best I can tell, my fast mind has what an economist would describe as a high discount rate, and so is unwilling to give up benefits now for larger benefits in the future. And I like cookies.